Electrical – How to increase the size of a subpanel to fit the breaker for a solar array

If you use a 100A breaker your main in the mobile home you will need #3 copper wire to feed the sub the sub panel. A 60 Amp breaker in the main panel should provide enough power from the loads listed this would require #6 copper wire.

You will need to run both hots a ground and neutral. In the sub the ground and neutral buses need to be isolated. Many times Panels come with the buses connected the connection will need to be removed or you can add a grounding buss screwed into the metal of the panel. (Make sure there is not a connection from the original buses to the box.)

I am hoping you will be living in the tiny house while remodel work is completed on the mobile. If both the mobile and the tiny house are used at the same time you may trip the main. If you trip the main you may have to do things like turn the AC off while the cook top is in use to prevent the main from tripping.

No, in fact if you don't NEED to use them, you should not. All breakers give off heat and cramming more breakers into a space not designed to handle that heat leads to things overheating.

Most panels now have to specifically ALLOW you to use tandem breakers and will LIMIT the number of them that you can use. This came about years ago because before that, people were overloading their panels and the heat was causing breaker failures and fires. So the designation is called "CTL", short for Circuit Total Limitation and all panels made since 1965 must now have that on the label IF you can install CTL listed tandem breakers. What that means is that in the mechanical workings of the panel and/or how the breakers attach to the bus (everyone does it differently), there are only a few spots where you can plug in CTL listed tandem breakers, because there is some sort of "rejection" clip or feature that prevents them from being installed anywhere else.

Unfortunately, a LOT of the breaker mfrs have not changed their basic designs since the 1960s, so if you manage to find breakers that are NOT CTL listed, that means they don't have the rejection feature and you can install them willy-nilly in the manner that caused the fire issues in the first place. As a general rule, you can't buy those breakers as new in hardware stores, but the internet has made this something that people can do again, even though they should not, and the issues are rearing their ugly heads once again. Inspectors will nail you on that if they see it in your panel, but that only happens when you take out a permit for something.